We're learning a lot about micro-climates and how small variations in temperature, humidity, wind, and other factors determine what grows best in a particular location. There's not much one can do about any of those factors, but there is something you can do that will have a positive impact, no matter where you live or what might be going on in Earth's biosphere: you can improve any garden anywhere by improving the soil. It's easy to do, the results are dramatic, and the benefits extend beyond your garden.
Sand, Silt and Clay: Texture is here to stay
The soil beneath your feet has a basic nature according to the geological history of your location and the type of “parent material” (rocks) from which it was formed. “Soil texture” is defined according to the percentages of sand, silt, and clay. This is good to know because different soil textures have different properties and will affect things like water filtration and nutrient availability. Soil texture does not include organic matter. Here's where things get interesting: you cannot change soil texture, but you can make major changes to how it functions by adding organic matter.
Imagine a pile of rocks, a bucket of sand or a lump of clay as various types of soil texture. Now imagine trying to grow something in any of them. Without organic matter, it's not going to happen. So, what is organic matter? Simply put, organic matter is anything that is alive, or was once alive: plants, animals, insects, microbes are all broken down by the microbial community. Organic matter improves the capacity of soil to infiltrate and hold onto water and nutrients, and this makes it possible for plants to grow and thrive.
Healthy Soil: It's like a good party
Soil with plenty of organic matter teems with life. Like a good party, there are lots of interesting guests (microbes such as bacteria and fungi. Also insects, etc.), plenty of good food and drink (available nutrients and water), enough room to move (loose, non-compacted soil), and plenty of action. Viewed through a powerful microscope, a handful of healthy soil would reveal billions of organisms doing their job. Although organic matter may only make up 5% of your soil, it is the 10% of microbial life in the organic matter that is essential for all soil functions like water infiltration, nutrient cycling, carbon sequestration and plant health.
At the other end of the spectrum is unhealthy soil. Like a ghost town, the microbial residents have vanished, and the place is dusty. It cannot infiltrate and retain water effectively and is easily eroded. This sad state can be caused by several things including no plant or mulch cover, repeated tilling, compaction, excessive use of chemical fertilizers, pesticides and herbicides.
How can I be sure my soil is healthy?
Effective use of organic materials such as compost can provide steady supplies of nutrients. This will create and maintain a desirable environment for the beneficial microorganisms that are essential for healthy soil. Did you know that leaving lawn clippings in place and allowing fallen leaves to remain is an effortless way to improve your soil? These are organic materials that break down quickly.
Keep it covered: Keeping soil covered with plants, leaves and organic mulch moderates soil temperature, conserves moisture, and prevents erosion while adding habitat and providing food for beneficial organisms. Remember all mulch eventually breaks down, so more needs to be applied either from leaves dropped by plants or from mulch applied by you.
Do not disturb: Avoid tilling or turning the soil. Instead, add a thin 3⁄8” layer of compost with a 2-3” layer of mulch on top and let nature do the work of aerating and opening things up. Be careful with leaf blowers by limiting their use to hardscape areas. This helps preserve valuable organic matter and topsoil and the beneficial microbes that live there.
Beyond the Garden Wall: Healthy soil has global implications
Carbon capture: Unlike carbon in the atmosphere, carbon stored in the soil is a good thing. Through a process known as “carbon sequestration,” soils can retain carbon in the form of organic matter, some of which is stable and some of which cycles. It is important to remember that plants and soil life are responsible for development of the organic matter that is held in soils. Recent studies show that soils alone trap about 25 percent of the world's annual fossil fuel emissions. So, if we want to sequester more carbon in the soil, we need more plants growing in a microbial diverse community.
Pesticide reduction: Just as healthy humans can more easily fight off diseases, plants grown in healthy soil are more naturally resistant to diseases. That means less reliance on pesticides.
Water efficiency: Healthy soil acts like a sponge: it holds onto water, so water is available to plants over an extended period. Good news for our climate with only winter rainfall. According to the USDA, every 1% increase in organic matter increases the soil's water holding capacity by as much as 25,000 gallons per acre. When water is stored in the ground, it also recharges groundwater. Healthy soil improves water quality by filtering out pollutants.
For more information on improving your soil, go to: https://marinmg.ucanr.edu/BASICS/SOIL_813/
For more help with your garden, ask a Master Gardener! Send your questions to mailto:firstname.lastname@example.org
This article was written by Maggie Mah (who is surprised to be so excited about compost) and edited by Cynthia Nations, Terry Lyngso, Kelly Torikai, Nancy Kruberg, and Nick Landolfi, SM/SF UC Master Gardeners.